Haptics is the scientific field that studies the sense of touch. In computing, haptics is the science and art of applying touch or force sensation to human interaction with computers. A haptic device gives people a sense of touch with computer generated environments, so that when virtual objects are touched, they seem real and tangible. An example is a medical training simulator in which a doctor can feel a scalpel cut through virtual skin, feel a needle push through virtual tissue, or feel a drill drilling through virtual bone. All of these types of interactions can feel almost indistinguishable from the real life interactions the simulator emulates. Haptics is applicable across many areas of computing including video games, medical training, scientific visualization, CAD/CAM, computer animation, engineering design and analysis, architectural layout, virtual toys, remote vehicle and robot control, automotive design, art, medical rehabilitation, and interfaces for the blind, to name a few. The word “haptics” derives from the Greek haptikos, from haptesthai, meaning “to grasp, touch, or perceive”, equivalent to hap(tein) to grasp, sense, perceive.
In computing, haptics can be implemented through different types of interactions with a haptic device communicating with a computer. These interactions can be categorized into the different types of touch sensations a user can receive—force feedback, tactile feedback, and proprioception (or kinesthesia).
With force feedback, a user can feel forces applied to a user's body by the movements of a haptic device, sensed by the user primarily through musculoskeletal forces, but also through the skin that touches the physical interface to a haptic device. This can be accomplished through a user's hand grasping a handle connected within the device to motors (e.g. 3D haptic devices, like the Novint Falcon, “NOVINT” and “FALCON” are trademarks of Novint Technologies, Inc., and 2D haptic devices like force feedback steering wheels and force feedback joysticks), and can also be implemented with haptic devices that a user puts a hand, arm, or leg into (e.g. a haptic glove or sleeve); vibrating motors within something that is held (e.g. a game controller or a force feedback mouse); a vibrating or moving object that a user sits on; or any other mechanical system that can give forces or touch sensations to a user. Haptics is often accomplished through electrical motors, although there are other methods to create force sensations such as with devices that are pneumatic (air controlled), hydraulic (fluid controlled), piezoelectric (materials that expand or contract with electric current), electric (sending currents directly to a users skin or nervous system), or which use passive braking systems.
With tactile feedback, a user can feel forces applied directly to the skin, which are detected by a user through sensors within the skin called mechanoreceptors. Tactile feedback can also be applied to a user through electrical currents applied directly to the skin or objects that can vary in temperature touching the skin. For example, tactile feedback can be accomplished with pin arrays on a haptic device on which a user places a hand or finger. The pins within the pin array can slightly raise or lower as the haptic device moves, giving a sensation that the user's finger or hand is moving across a virtual object with texture.
Proprioception is the sense of where one's body is in space. For example, if you move your arm out to the side, even if your eyes are closed, you know where it is. Our sense of proprioception is derived from the forces our muscles exert within our body. Force feedback generally has a proprioceptive component, as a user's movements of a haptic device in correlation with an application create the forces one feels. Even computer input devices that are generally not considered haptic devices use our sense of proprioception, such as mice and keyboards. Kinesthesia is similar to proprioception, in that it is a sensation of strain in muscles, and through it we know our body position, but kinesthesia also includes other internal feelings such as the feeling of a full stomach.
Haptic devices have varying complexities, and can move in different ways. Force feedback devices are often described by their Degrees of Freedom (DOF). A Degree of Freedom refers to a direction of movement. Common Degrees of Freedom include right-left movement (X), up-down movement (Y), forwards-backwards movement (Z), roll (rotation about the Z axis), pitch (rotation about the X axis), and yaw (rotation about the Y axis). Degrees of Freedom can refer both to how a device keeps track of position, and how a device outputs forces. A mouse, for example, is a 2 DOF input device—it keeps track of position in the right-left Degree of Freedom, and the forward-backward Degree of Freedom. A joystick is also a 2 DOF device, but its Degrees of Freedom are different (it rotates forwards-backward, and right-left). A force feedback joystick is a 2 DOF device with force feedback. It both tracks 2 DOF and gives simple forces in 2 DOF. The Novint Falcon is a 3 DOF force feedback device. It tracks in 3 DOF (right-left, forwards-backwards, and up-down), and has actuators and an onboard controller that can supply forces in those same Degrees of Freedom. 3 DOF devices (and higher DOF devices) are significantly more complex than 2 DOF devices.
Interface devices with input-only operations generally pose little risk to users. Incorrect input can result from device failures or communications failures, but such failures do not generally directly endanger the user. A haptic device, in contrast, can exert forces on the user. Such forces, if improperly controlled, can damage the device itself and can endanger the user. For example, a haptic device might be erroneously commanded to apply maximum forces in a way that causes the device to exceed its force or velocity constraints, damaging the device. As another example, a haptic device might be erroneously commanded to suddenly change the forces presented to the user, causing injury to the user. As another example, a haptic device might be erroneously commanded to suddenly shift from maximum resistance to motion by the user to maximum forces in the direction of motion by the user, causing the device to reach a limit of its range of motion at high speed and with high forces, damaging the device and potentially injuring the user. Such unsafe conditions can arise from many sources. As an example, a communications failure such as a failed or damaged communications channel can cause commands or device status reports to be lost or corrupted. As another example, software that is not correctly configured can attempt to communicate with a haptic device. As another example, a haptic device with unexpected capabilities or limits can be connected to a host computer, and can respond in unexpected ways to commands intended for another type of haptic device. The potential risks associated with a haptic device can make it more important that all aspects of the control of and communication with the haptic device be robust and safe.
The computer industry has developed many communications standards. Contemporary standards generally address issues such as connectors, electrical requirements, cable performance, and bit-level protocols. Contemporary standards can provide high speed, high reliability, and cost-effective communications. They do not, however, provide safety and security that can be desired for safe and efficient operation of haptic interface devices. Accordingly, there is a need for communications methods, and haptic and host computer implementations of such methods, and systems comprising one or more haptic devices and one or more host computers using such methods, that combine the advantages of contemporary standards with safety and security desired for haptic interfaces.